This invention relates to a magnetic read/write head for a floppy disk drive system.
Currently, two types of floppy disk drive systems available are a single-sided head type, in which a magnetic read/write head (hereinafter referred to as a "head") is fixed on one side of a floppy disk (hereinafter referred to as a "disk"), and a double-sided head type in which the heads are provided on both sides of the disk. The invention pertains to the double-sided head type.
In current two-headed type disk systems there are inherent problems which result from the disk being warped or transformed from a straight planar surface to one having a complex curvature. This transformation of the disk results in the heads not being positioned properly on the disk and thus not reading or playing accurately. The problems inherent with the prior art double-sided head type disk drives can be better understood with reference to FIGS. 1, 2 and 3.
FIG. 1 depicts conventional double-sided heads each in contact with a disk which is held between the heads. In FIG. 1, the left-hand side is that closest to the inner circumferential track of the disk (the side closest to the center of the disk and hereinafter referred to as the "inner side") and the right-hand side of FIG. 1 is the side of the outer circumferential track of the disk (hereinafter referred to as the "outer side"). An upper head 1a and a lower head 1b are in contact with a disk 8 being held therebetween. The contacting plane 2 of the heads 1a and 1b with disk 8 is usually divided into two portions by a groove 7. In some instances, groove 7 is provided on both heads, in others, groove 7 is provided on only one of the heads and in still other cases, no such groove is provided in either head. A faceted portion 3, called a chamfer, is provided at the rim portion of the contacting plane of each head, which continues to the side surface of the head.
According to current industrial standards for the floppy disk, a gap center 6a of the upper head is formed closer to the inner side of disk 8 than the gap center 6b of the lower head by a certain distance. In other words, in general, with the upper and lower heads aligned, gap 6a of upper head 1a is positioned closer to the inner side of disk 8 and gap 6b of lower head 1b zis positioned closer to the outer side of disk 8. However, the instant invention applies to both the case where the gap of the upper head is positioned closer to the inner side of the disk than the gap of the lower head, as is usual, and to the case where the gap of the upper head is positioned closer to the outer side of the gap than that of the lower head. In the following description, only the former case which is commonly used is referred to for brevity and simplicity. However, the description is also applicable to the latter case if the terms "upper" and "lower," and "high" and "low," respectively, in the description are exchanged. Heads 1a and 1b are commonly fixed to a pair of gimbal springs 4a and 4b (hereinafter referred to as the "gimbals"), respectively, which, in turn, are secured to a pair of carriages 9a and 9b, respectively. Lower carriage 9b is usually mounted on the frame of the floppy disk drive system via the guide shaft 11.
The prior art head constructions are provided with various combinations of upper and lower gimbals. In one embodiment, the heads attached thereto are allowed to rotate in two directions, that is, in the direction along the radius of the disk and in the direction along the tangent line of the circumference of the disk. In other embodiments, the upper gimbal allows the head to rotate in two directions while the lower gimbal allows the head to rotate in only one direction, or the upper gimbal allows the head to rotate in two directions while the lower gimbal fixes the head. The rotatable gimbals are supported by a pivot 5 from behind and are rotatable around the pivot 5, thereby adjusting to the deflection or shaking of the disk to achieve accurate reading and recording.
FIG. 1 shows the ideal condition of the contact between the heads 1a and 1b and disk 8. In practice, however, the heads are generally positioned higher or lower than the proper position for holding the disk. Also, since the rotating disk between such heads is fairly hard and shaped like a film, partial transformation such as flexing of the disk occurs. Thus, the disk distorts in a complex manner between the upper and lower heads during operation, as shown by FIGS. 2 and 3. The conditions of the contact between heads and disk of FIGS. 2 and 3 are described below. In this discussion, the position of the head that accurately coincides with the proper location of the disk (FIG. 1) is referred to as the "reference position" of the head.
FIG. 2 shows the case where head 1a is pushed up by the distorted disk 8 to a position are higher than the reference position, and consequently, higher than the position of the lower head 1b. As is shown in FIG. 2, disk 8 distorts along a complex curve between the heads due to the above-mentioned factors. To be specific, in the example of FIG. 2, disk 8 extends upwardly from a point of contact 2c with lower head 1b, pushing upper head 1b upwardly. Point of contact 2c is located on the inner side (hereinafter referred to as the "inner edge") of contacting plane 2 of lower head 1b. The distorted disk 8 contacts the upper head at point 2f and bends downwardly toward the lower head to contact the lower head. Then, the disk bends upwardly toward the upper head again, contacting upper head 1a at point 2g, and finally extends out from the outer side of the head. As is apparent from FIG. 2, on the inner side, the contacting point 2f of the disk and the upper head is likely to be closer to the center of the disk but not at gap 6a. On the outer side, the disk contacts the upper head again at a point near the outer side of the plane of the head. Accordingly, the output of the upper head is much more unstable than the output of the lower head. Thus, the allowable range of the head position over which satisfactory output can be obtained from both of the upper and lower heads is limited by the upper head condition as above.
The allowable range of the head position is one of the values quantatively expressing the condition of the contact between the head and the disk, as is illustratively explained by FIG. 4. FIG. 4 is a graph showing the relative change of the output of the heads when the head position is shifted with respect to the reference position. The range of the head position over which the output is larger than the lowest limit 12 of the acceptable output is called the allowable range of the head position, which is the hatched area 13 in FIG. 4.
When disk 8 is distorted, as shown in FIG. 3, upper head 1a is pushed down and the disk and is lower than the reference position. Specifically, the disk is contacted by the inner edge 2h of the contacting plane of upper head 1a, then contacts lower head 1b and then contacts both the upper and lower heads in the region 2i near the outer edge of the heads.
In this case, the disk likely contacts the upper head not at gap 6a of upper head 1a, but at a point closer to the outer side of the disk than the upper head gap. Accordingly, the output of upper head 1a is lower than that of lower head 1b and the allowable range of the head position is limited. Moreover, the output of lower head 1b also tends to be reduced by the increased distortion of the disk.
The above problem may be improved to a certain degree by varying the distance between the inner edge of the upper head and the gap of the upper head, although such a method is not a thorough solution of the problem. One reason for this is that if the distance therebetween is increased, the width of the head in the direction of the radius is increased. Consequently, the tolerance of the relative inclinations of the head with respect to the disk decreases, which leads to a difficulty of mass production and the rise in the manufacturing cost.
Furthermore, in the conventional head mechanism, if the distance between the gap of the upper head and the inner edge of the upper head is increased, the distance between the gap of the upper head and the inner edge of the lower head is necessarily increased. Under such condition, if the head is located higher than the reference position, the contact between the upper head gap and the disk is insufficient as described previously. Thus, the desirable conditions when the head is higher and when the head is lower than the reference position are incompatible so that the allowable range of the height of the heads is not expanded.
Reference is now made to FIG. 5 which is a top plan view of the contacting plane of lower head 6b, by way of an example. By examination of the contacting condition between head 6b and the disk 8 of a system using the head of FIG. 5, it has been found that the head and the disk do not contact most intimately near the gap of the head, but rather, contact most intimately at the four corners and at the inner edge of the head. The positions having the most intimate contact are contact regions 17, shown enclosed by the broken lines in FIG. 5. Where, as shown in FIG. 5, the head and disk do not necessarily contact intimately at the gap of the head, the output of both of the upper and the lower heads likely becomes unstable and insufficient.
Moreover, in the double-sided head system, another problem generally arises due to the rigidity of the disk, namely, when the disk is higher than the reference position, the rigidity of the gimbal and the disk balance to cause the upper head to incline to the outer side to some degree as shown by FIG. 2. Under such a condition, if the distance g between gap 6a of lower head 1b and the outer edge of upper head 1a is large, the space between the upper and the lower heads near the lower head gap is large. Accordingly, the pressure by the upper head on the disk is insufficient and close contact between the lower head gap and the disk is not obtained.
Thus, it is necessary to decrease the distance g until the disk and the lower head gap contact each other intimately. However, in the case where the side lines of the upper and the lower heads are on the same line as in the conventional systems, when the head is not at the reference position, an upward distortion of disk 8 to the position shown by dashed line 10 in FIG. 2 is observed to occur near the edge of the outer side of the contacting plane of lower head 1b. This distortion 10 of the disk pushes up the upper head and reduces the output of the lower head.
The problems in the prior art described above may be summarized as follows:
First, when the upper head is higher than the reference position, intimate contact between the head and the disk is usually obtained at a position toward the inner side with respect to the upper head gap and the output of the upper head deteriorates.
Second, when the upper head is lower than the reference position, intimate contact between the head and disk is usually obtained at a position toward the outer side with respect to the upper head gap and the output of the upper head deteriorates.
Third, the conventional head contacts the disk most intimately not at the gap, but at the four corners of the contacting plane of the head and at the inner edge thereof.
Fourth, if the upper head is higher than the reference position, the distortion 10 of FIG. 2 of the disk occurs near the outer edge of the contacting plane of the lower head with the disk.
As mentioned above, in the conventional double-sided head systems, there are many times when the output of the upper head deteriorates with respect to the output of the lower head. Accordingly, the allowable range of the head position is greatly limited by the upper head. This is specially true, in the case of small-sized and high-density disks such as those of 3.5 or 3 inch type, having a hub made of metal or hard plastic provided in the center part of the disk in order to improve the accuracy of addressing the tracks. Since such a hub occupies the portion very close to the innermost track of the disk and the radius of the track is small, the rigidity of the disk affects the contact between the head and the disk. As such a disk of high rigidity is formed as a film, the distortions of the disk, as mentioned before, occur very frequently and the contact between the head and the disk and the output between the heads are largely affected. The quality of the contact between the head and the disk and the output of the heads depend primarily, on the effect of such distortions of the disk. In high-density magnetic recording and reproducing, the present acceptable range of the space between the head and the disk is less than 0.2 microns. In the conventional head system, a space between the head and the disk not within the above range is easily produced. Thus, a system using small disks, such as those of the 3.5 or 3 inch type, or disks on which the magnetic layer is a metal film formed by an evaporation or sputtering process, is significantly affected by the high rigidity of the disk. This results in the contacting condition between the head and disk being poor and unstable.
Accordingly, when the conventional head is used for such disks, it is necessary to position accurately the head and to restrict the inclination of the head and, even then adjustment of the position of the head with respect to the disk is sometimes necessary. The requirements as above cause the manufacturing cost of the drive system to increase.